The gas constant (also known as the molar, universal, or ideal gas constant, denoted by the symbol R or R) is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation. It is equivalent to the Boltzmann constant, but expressed in units of energy (i.e. the pressure-volume product) per kelvin per mole (rather than energy per kelvin per particle).
Its value is
The two digits in parentheses are the uncertainty (standard deviation) in the last two digits of the value. The relative uncertainty is 1.8 × 10−6.
The gas constant occurs in the ideal gas law, as follows:
where p is the absolute pressure, V is the volume of gas, n is the number of moles of gas, and T is thermodynamic temperature. The gas constant has the same units as molar entropy.
| Values of R [1] | Units (V P T −1 n−1) |
|---|---|
| 8.314472(15) | J K−1 mol−1 |
| 1.9858775(34) | cal K−1 mol−1 |
| 8.314472(15)×107 | erg K−1 mol−1 |
| 8.314472(15) | L kPa K−1 mol−1 |
| 8.314472(15) | m3 Pa K−1 mol−1 |
| 8.314472(15) | cm3 MPa K−1 mol−1 |
| 8.314472×10−5 | m3 bar K−1 mol−1 |
| 8.205746×10−5 | m3 atm K−1 mol−1 |
| 82.05746 | cm3 atm K−1 mol−1 |
| 84.78402×10−6 | m3 kgf/cm2 K−1 mol−1 |
| 8.314472×10−2 | L bar K−1 mol−1 |
| 0.08205746(14) | L atm K−1 mol−1 |
| 62.36367(11) | L mmHg K−1 mol−1 |
| 62.36367(11) | L Torr K−1 mol−1 |
| 6.132440(10) | ft lbf K−1 g-mol−1 |
| 1,545.349(3) | ft lbf °R−1 lb-mol−1 |
| 10.73159(2) | ft3 psi °R−1 lb-mol−1 |
| 0.7302413(12) | ft3 atm °R−1 lb-mol−1 |
| 998.9701(17) | ft3 mmHg K−1 lb-mol−1 |
| 1.986 | Btu lb-mol−1 °R−1 |
